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cleveland
05-22-2002, 05:57 AM
I need some help figuring out the sorce of vibration in my 12jg. it has a new rebuild kit installed by a local shop that cant seem to get it right. iam in OK. and when you say jet boat people get a funny look on their face. the vibration seems to be worse around 2000rpm. its in a 21foot tunnel hull powered by 454 any sugestions. thanks
Licketty Split
05-22-2002, 06:18 AM
is the impeller new ? if so check the shaft for straightness
cleveland
05-22-2002, 07:18 AM
yes the impeller is new i dont have a dail indcator, but I can borrow one will let you know. thanks
cleveland
05-23-2002, 06:26 AM
the imprller is 7 thousands out. i understand from the factory it would be 2 to 3 out. is .007 enough to cause exssive vibration.
Licketty Split
05-23-2002, 06:42 AM
What does te shaft read? if it is in the shaft it will definetly vibrate. With a new imp. I think its more lickly in the shaft. Some times the shaft can be trued on a leith Next if it is true it is a balance issue send the Imp back for a replacement or balance it. also look at your U joints and motor angle.
cleveland
05-30-2002, 03:17 PM
I would have been sooner but my server has been out. i mis spoke the other day. yes it is the shaft thats .007 out. ive taken the boat back to the shop to make them stand by their work which does not seem to a problem, iam happy to say. the mec said he adjusted the motor and it doesnt hardly vibrate any more i find this hard to beleave knowing the shaft is this far out. i had him check it and he said it was .005 to .009 out.
Licketty Split
05-31-2002, 02:47 PM
I dont know I think I would have it trued up or replaced but you could slways try it first
Max_182
06-01-2002, 08:25 AM
I'd look at the U-joint or whatever you use to connect to the crank. If it didn't vibrate before the rebuild I'd suspect the coupling. And I don't think .007" is enough to vibrate that hard. I've run impellers with large chunks missing will little noticeable vibration.
HOSS
06-01-2002, 09:56 AM
I second that. Look at u-joints and motor angle.
jet496
06-01-2002, 11:10 AM
I had a friend (who owns an auto mechanic shop) recently put a new shaft, impeller, etc on. He checked the shaft & found it to be .007 out. He sent it back & got another the same. Finally the guy he bought it from hand picked one for him.
What I'm getting at is I think it's normal unless you're running high RPM's for racing you shouldn't notice it. I'll bet most boat shafts are off that much or more, but how many people actually check them.
Eric455
06-02-2002, 12:22 AM
get your crank, flyweel, and pully balanced and it will go away
hack job
06-02-2002, 08:55 AM
some times impellers arent ballance properly and that owuld cause some vibrations i know that its new but if you this it could be .007 off then it is most likley out of blance too. just a thought, i know this is a big deal with big motors. http://free.***boat.net/ubb/wink.gif
Tyson www.plumbersassracing.com (http://www.plumbersassracing.com)